You are in a car and there is a pendulum suspended in front of you. You have no idea of what is going outside, i.e., you are completely blind from the surroundings. You can see only the pendulum and the interior of the car which has nothing else. You find that the pendulum is at the beginning straight down and later you find that it is bending towards you. (I hope you understand) Can you conclude that the car is accelerating?